function change_exp (selectObject) {
    var new_id = selectObject.options[selectObject.selectedIndex].value;

	for (var i=0; i<1000; i++) {
		var optionObject = selectObject.options[i];
        if (optionObject == null) {
			break;
		}
		var id = optionObject.value;
		var element = document.getElementById(id);

		if (id == new_id) {
			element.style.display = 'block';
			element.style.visibility = 'visible';
		} else {
			element.style.display = 'none';
			element.style.visibility = 'hidden';
		}
	}
}